The present invention relates to a device for detecting an amount of exposure in a copying machine.
In prior art copying machines, the optical system for exposure, namely, the lenses, mirrors and lamps, tend to gradually become contaminated by the collection of toner powder and other dust in the machine. As a result, the amount of exposure may be insufficient or the copy foggy; that is, the resultant copy may be unsatisfactory in quality.
In order to solve the above-described problem, a device has been proposed in the art in which a reference reflection surface is provided near the platen and the amount of light reflected from the reference reflection surface is detected to correct the amount of exposure of the lamp. Such a device is shown in FIG. 1.
As shown in FIG. 1, a reference reflection surface 2 is provided at a predetermined position on a platen 1 and is illuminated by a lamp 3 during exposure. Light reflected from the surface 2 is applied to a photosensitive drum 7 by means of a mirror 4, an image forming lens and a mirror 6. A light receiving sensor 9 is disposed near the photosensitive drum 7 and is mounted in such a manner that it can be disposed either in or out of the optical path by operation of a driving device such as a solenoid 8. The light receiving sensor 9 detects the amount of light received from the reference reflection surface 2, from which the amount of light emitted by the exposure lamp 3 can be corrected.
The above-described conventional approach is disadvantageous in that, as the provision of a driving mechanism is required in order to cause the light receiving sensor to move in and out of the optical path, the manufacturing cost of the copying machine is high due to the need for such a mechanism. Further, if the light receiving sensor itself becomes contaminated, it is difficult to accurately detect the state of the optical system in the copying machine.
Accordingly, an object of the invention is to provide an exposure detecting device for a copying machine in which no such driving mechanism need be provided, and the above-described difficulty related to the contamination of the light receiving sensor is eliminated.